Sustainable bio-char-based ink having conductive properties

ABSTRACT

A process for forming a conductive hemp-based ink comprising carbonizing hemp and reducing the particle size of said hemp via a milling process to between 2 and 5 microns, wherein said reduced size hemp particles are combined with at least one aqueous carrier to produce an ink, and wherein said ink is conductive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/838,966 filed on Apr. 26, 2019, with the UnitedStates Patent and Trademark Office, the contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present application is generally related to processes and methodsfor forming sustainable ink materials comprising charred or carbonizedhemp particles. The ink may be specifically crafted to have enhancedconductive and capacitance properties or nonconductive properties,depending on the formulation. Furthermore, the materials may serve as apigment for sustainable ink products.

BACKGROUND OF THE INVENTION

Ink, by its very nature is nearly as old as written language.Historically, ink combines a carrier and a pigment to form a liquidmaterial. Early inks utilized natural materials and pigments weregenerated from leaves or berries to form a variety of colors. Thepigment is admixed with a carrier, applied to a surface, and the carrierevaporates or is absorbed into the surface, leaving the pigment. Whenthe ink dries, the pigment is left on the surface.

Char has also been used to make ink for centuries. Char is typicallymade by heating a cellulosic material in a low oxygen environment at atemperature of between 600-700° C., with higher temperatures unnecessaryfor current processing needs. This process typically takes between 12-72hours, though longer periods are possible, and the process burns offvolatile compounds such as water, methane, hydrogen, and tar. Incommercial processing, the burning takes place in large concrete orsteel silos with very little oxygen, and the burning stops before thematerial turns to ash. The process yields black lumps and powder, about25% of the original weight.

Historically, char referred to charcoal, which was used for cooking andheating. The process of making charcoal is ancient, with archaeologicalevidence of charcoal production going back about 30,000 years.Individuals utilize cellulosic matter, which is burned or charred at lowoxygen conditions, to generate charcoal. When ignited, the carbon incharcoal combines with oxygen and forms carbon dioxide, carbon monoxide,water, other gases, and significant quantities of energy. The quantityof energy is the salient feature as charcoal packs more potential energyper ounce than raw wood. Furthermore, charcoal burns steady, hot, andproduces less smoke and fewer dangerous vapors than raw wood. Becausecharcoal burns hotter, cleaner, and more evenly than wood, it was usedby smelters for melting iron ore in blast furnaces, and blacksmiths whoformed and shaped steel, among other uses.

Interestingly, as wood and other cellulosic materials are carbonized,the material structurally changes into simple carbon structures. Thishas been historically utilized for its absorptive properties, forexample in filtering wastewater as well as binding body toxins. Largeamounts of carbon are utilized for these purposes in numerousindustries.

Carbon products based on hemp have heretofore been neglected. Thisneglect is due to numerous reasons including the significantdifficulties with the plant's mechanical structure, generation of stickyresin substances on the stalk during retting, its light mass anddensity, and presence of certain metabolites and cannabinoids, whichhave generally precluded its use.

The processes and methods described herein advantageously provide newmethods and processes to generate micron-sized particles from hemp-basedcellulosic materials, which are advantageously utilized to formhemp-based inks.

SUMMARY OF THE INVENTION

A process for generating a hemp char-based ink comprising a carrier anda portion of hemp-based char, wherein said ink is conductive; theprocess comprising charring hemp stalk at a temperature of at least1100° C. under low oxygen conditions to create a char; milling said charto create a milled char and adding said char to an aqueous carrier; saidaqueous carrier further comprising at least one other solid, and atleast one other excipient for stabilizing the hemp char.

In a further embodiment, a method for making a non-petroleum based blackink, said ink comprising an aqueous carrier and a pigment made fromcharred hemp; said charred hemp made by charring hemp stalk at atemperature of at least 1100° C. under low oxygen conditions to create achar; milling said char to create a milled char to between 2 and 5microns, and adding said char to said aqueous carrier.

In a further embodiment, the method wherein the milled char isclassified with a classification system having at least one gradient of2 microns in size and a second gradient of 5 microns in size; andcapturing the material between about 2 and about 5 microns in size foraddition to the hemp-based ink.

In a further embodiment, the method wherein the milled char is between 1and 19 weight percent of the total weight of the ink.

In a further embodiment, the method wherein the milled char comprisesbetween 1 and 5 weight percent of the ink to function as a pigment andbetween 14 and 19 weight percent wherein the ink is conductive whenscreen printed with an 86 to 110 size screen.

In a further preferred embodiment, a method of making a conductivehemp-based ink comprising: carbonizing a portion of hemp in a furnace,said furnace being flushed with nitrogen and then heated from 25° C. togreater than 1100° C., holding the temperature of greater than 1100° C.for at least 60 minutes; maintaining nitrogen flow over the heating andhold times to maintain a low oxygen environment; removing the hemp fromthe furnace and cooling it to room temperature; milling the cooled hempto a reduced particle size and classifying the milled hemp, obtaining afraction from the classified hemp, wherein a 95% of the milled hemp isbetween 2 and 5 microns in size; combining the classified hemp with anaqueous carrier to form the conductive hemp-based ink.

In a further embodiment, the method wherein the conductive hemp-basedink comprises between 1 and 19 weight percent of the weight of the inkand is printed using a size 60 printing screen.

In a further embodiment, the method wherein the conductive hemp-basedink comprises between 14 and 19 weight percent of the weight of the inkand is printed using an 86 to 110 size printing screen. In a furtherembodiment, the method wherein the conducive hemp-based ink is washableand retains conductivity after washing.

In a further embodiment, the method wherein 99% of the milled hemp isless than 5 microns in size.

In a further embodiment, the method further comprising adding at leastone solvent to the aqueous carrier, wherein the solvent evaporatesfaster than water.

In a further embodiment, the method wherein the carrier furthercomprises an excipient selected from the group consisting of: abuffering agent, a resin, humectant, a fungicide, a surfactant, abiocide, a bulking agent, a dispersing polymer, and combinationsthereof.

In a further embodiment, the method wherein the milling step is a wetmilling process. In a further embodiment, the method wherein the wetmilling process comprises addition of a solvent added to a millingchamber with cooled hemp at a ratio of hemp to aqueous solvent from 10:1to 1:10. In a further embodiment, the method wherein the solventutilized in the wet milling process is a nonaqueous solvent. In afurther embodiment, the method wherein the solvent utilized in the wetmilling process is an aqueous solvent.

In a further embodiment, the method wherein the ink further comprises alinear or branched chain alcohol. In a further embodiment, the methodwherein the liner or branched chain alcohol is a C₁-C₁₀ alcohol.

In a further embodiment, a sustainable ink comprising an aqueous carrierand a non-petroleum based carbon pigment made form hemp char; said hempchar produced by charring hemp at at least 1100° C. under nitrogen gasfor a period of at least 60 minutes; and wherein said hemp char ismilled to yield a milled char; wherein the milled char is classifiedusing a classification system to yield a fraction of classified charbetween 2 and 5 microns in size; wherein the classified char is added tothe carrier at between 1% and 20% of the total weight of the ink.

In a further embodiment, the sustainable ink of claim 18, wherein theink is conductive when printed with a 60 screen size and at aconcentration of at least 1 weight percent.

In a further embodiment, the sustainable ink wherein the ink is suitablefor screen printing with a size 60 screen, and wherein the classifiedchar comprises between 1 and 6 weight percent of the weight of the ink,which yields a non-washable conductive ink.

In a further embodiment, the sustainable ink wherein the classified charcomprises between 14 and 19 weight percent of the weight of the ink, andwherein the ink is washable upon screen printing with a screen size ofbetween 86 and 110, and remains conductive after washing.

In a further embodiment, an ink comprising a portion of hemp char and atleast one carrier; said hemp char produced by charring hemp at least1100° C. under nitrogen gas for a period of at least 60 minutes; andwherein said hemp char is milled to an average particle size of between2 and 5 microns via a milling process; wherein the hemp char is added tothe carrier at between 1% and 20% of the total weight of the ink and isdispersed into the aqueous vehicle; a dispersing agent or a surfactant;and at least one binding agent.

In a further embodiment, the ink comprising between 1 and 20% hemp char,wherein said ink is screen printed onto a surface and imparting a UPF ofat least 20.

In a further embodiment, the ink comprising a hemp-based pigment, saidpigment comprising at least 10% less PAH than a petroleum-based carbonof the same concentration.

In a further embodiment, the ink of any of the above methods, whereinthe ink is non-toxic.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a flowchart of a milling process for char to form an ink.

FIG. 2 depicts a classification system.

FIG. 3 depicts a wet milling process for milling hemp and forming anink.

FIGS. 4A and 4B depict images of carbon made in a shape for mosteffective ink.

FIGS. 4C and 4D depict images of “flat carbon” particles found in priorart.

FIG. 5 depicts data regarding dry crocking of test samples using a hempcarbon-based ink.

FIG. 6 depicts data regarding wet crocking of test samples using a hempcarbon-based ink.

FIG. 7A depicts data regarding hemp carbon ink conductivity at variouspercentages of carbon by weight.

FIG. 7B depicts data regarding hemp carbon ink conductivity at variousscreen sizes and percentages of carbon by weight.

FIGS. 8A and 8B depict conductive of ink after laundering with FIG. 8Aregarding a 15% hemp carbon sample and FIG. 8B regarding a 20% hempcarbon on three different materials.

FIGS. 9A-9C depict samples for UV testing of ink.

DETAILED DESCRIPTION OF THE INVENTION

Hemp serves as the raw material for a generation of the hemp-basedbio-char. Growth of hemp is predicated on simply growing biomass. Hemphas a long history of industrial use and was widely cultivated in theworld for its rough use for fibers. Hemp has many advantages over otheragricultural crops, namely, the plant itself is resilient to weeds, itcan be harvested 2-3 times a year and it does not need pesticides orherbicides to flourish. Its deep root system means that hemp plants needless nitrogen (fertilizer) and water to flourish. Moreover, farmers canuse hemp plants as an alternative to clear fields for other crops. Theaverage hemp plant grows to a height of between six (6) feet to sixteen(16) feet and matures in approximately seventy (70) to one hundred ten(110) days, thus facilitating multiple harvest opportunities each yearin many areas of the world. A hemp crop has the potential of yielding3-8 tons of dry stalks per acre per harvest while remaining carbonnegative.

The hemp can be taken from any of the various cultivars of the Cannabisfamily, particularly from the Cannabis Sativa plant, and biowaste fromhemp growth can be utilized. In this manner, we can capture biomass fromother industries that are simply interested in processing seeds or leafygreens and utilize both the fibers and hurd. Indeed, herein, processesare described that can utilize both the fibers and hurd in higher valueapplications than the prior uses. The processes herein describe that itis preferential to utilize both the fiber and the hurd together, inorder to generate a superior char material. Heretofore, hemp fibers weretypically separated from the hemp hurd, and the fibers used for certainmaterials and the hurd and remaining biomass utilized in low valueapplications, such as concrete fillers, animal bedding, and otherapplications, including simply being composted or burned as waste.However, the combined processing reduces waste and utilizes the fibersand hurd together an a more efficient and valuable process.

Hemp, like many dicotyledonous plants, contains a phloem (hurd) andfibers (bast fibers) around the phloem. The fibers may be separated fromthe hurd by mechanical action (for example, decortication), or chemicalaction, and the fibers can then be used for any fiber materials,including textiles like carpet, yarn, rope, netting, matting, and thelike. The hurd, by contrast, has previously only been used for roughprocesses such as papermaking, particleboards, concrete mixtures, andconstruction composites, as well as for animal bedding. In any givenhemp plant, there is significantly more hurd biomass than of fibers.Unfortunately, the use of the hurd has been shunned to date, even thoughit is the primary biomass of the plant. Manipulation and use of thehurd, therefore, would serve as a critical step in use of thiscellulosic product that would otherwise become waste.

The singular use of fibers, however, leads to large amounts of wastebyproduct from the stalk or hurd and limits viability of the plant forwidespread cultivation. Furthermore, the concern regarding the amountsof tetrahydro cannabinoids (THC) dramatically reduced its use in theTwentieth Century. There are a number of different strains of the hempplant that contain smaller and larger amounts of the psychoactivecompound, THC, and thus cultivation can be optimized for the particulargrowth and THC content that is desired. Here, low to zero THC, a fastgrowth rate and a high total biomass is desired. These traits may benaturally derived through strains and crossbreeding as known to those ofordinary skill in the art, or genetically modified.

The relative environmental sustainability of hemp compared to manycommon agricultural crops, such as cotton, wool, and flax, utilized inthe production of fibers for fabrics and industrial materials is wellestablished. As an alternative to wood pulp, hemp grows faster and maybe able to be grown in areas that are not hospitable to trees, making itpotentially possible to use locally grown hemp in a variety ofmaterials. Furthermore, unlike harvested trees, hemp retains absorbedcarbon, rather than releasing it back into the atmosphere. Accordingly,hemp functions as a carbon negative plant, making it highly attractivefor large scale use, especially where a downstream use can beidentified. These features make hemp an intriguing option forcultivation, but the many difficulties with the plant have precluded itsuse on any scale up to this point. What is missing from the hempecosystem are processes and methods for consumption of the hemp materialafter its growth, wherein the fibrous materials of the plant can beutilized in commercially viable enterprises.

Therefore, in an effort to pursue sustainable and environmentallyresponsible bio-char material, suitable for use in a variety of batchprocesses, and as a replacement for the petroleum based carbons, whichare expensive and time/process intensive, such as CNTs and graphenes,applicant has identified micron particle bio-char hemp-based materialsand processes for generating the same, in which the bio-char is formedwith a carrier into a pigment or a conductive ink. This allows forunique printing opportunities on materials.

Bio-char produced from the pyrolysis of cellulosic agricultural wasteresults in amorphous carbonized solids that exhibit similar electricalproperties of CNTs. Herein, the methods, processes, and products utilizecarbonized hemp as the cellulosic material to create a carbon-based inkhaving particle size of typically less than 5 microns. As used herein,the size “less than 5 microns” or “less than x microns,” where x is aninteger, means that the size of the particle is less than the statedinteger for the major axis of the material. The major axis being thelongest length of the particle. So, a particle that is 3.5 microns inlength, 1.5 microns wide, and 0.2 microns tall, would be “less than 4microns in length,” as the length of the major axis is 3.5.

In producing carbonized materials, it is impossible to create identicaland regular particle shapes, and thus, under microscopic imaging, theparticles will vary in shape and size. However, in preferred embodimentsthe particle size is preferably below 5 microns, and preferably between2 and 5 microns, which can be sorted using a classification system. Oncesuch material is generated, the micron-sized char can be added to acarrier and suitable excipients for generating an aqueous-based ink.

Interestingly, the carbon utilized in these processes and in, forexample, screen printing, is optimized when the carbon is particularshaped. Typical carbon materials are long and flat, and while they havea 3-dimensional characteristic, the length is typically 3 times to 1000times of the width, and typically the length is 5 times to 10,000 timesof the height. In comparison to the typical long and flat particles, theprocess herein creates particles that are more consistent in dimensionsbetween the length, width, and height. This results in a particle that,while not having an organized shape, has a length in each of the three(3) axes (x, y, z) that is closer in size than the typical grapheneparticle. Thus, where a flat carbon (graphene) of the prior art wouldhave a length of 5 microns, a width of 5 microns, and a height of 0.01micron, for example, the claimed carbon would not have the samediscrepancy with regard to differences between the longest and shortestaxis. An example particle could have a length of 1.5 microns, a width of1.0 microns, and a height of 0.1 microns. Herein, this carbon, havingsimilar dimensions shall be referred to as a 3D carbon, referring to itsrelatively size in three dimensions.

FIGS. 4A-4D depict images of the 3D carbon and of graphene. Notably, the3D carbon is of smaller size, is more consistent in the size in relationto the other particles, and is less flaky (i.e., the material is not aslong and thin) as the prior art carbon. The hemp-based material thus hasa narrower bell curve and the particles themselves are more consistentin their size ratio between the major axis (the longest length) and theminor axis (the shortest length) for each particle on average, ascompared to the prior art.

Hemp based carbon materials are derived from hemp stalk and other hempfibers. The hemp material is preferably utilized within a specificwindow after harvest to prevent the natural separation of the fiber fromthe hurd, which leads to the formation of sticky residues that impactthe efficiency of postprocessing. This sticky resin material, onceformed, reduces the ability to efficiently char the hemp, and furtherreduces the yield of milled char that is generated under 2 microns insize. Accordingly, after cutting the hemp stalks they are dried,preferably in a controlled manner, for example in a drying room orchamber, that evenly allows for drying and reduces retting and growth ofmold or fungus. However, it may be suitable to cut the hemp and allowthem to dry on the field for 0-7 days and/or collecting them andfinalizing the drying process in a controlled environment.

Processing of the hemp may include one or more steps. In the simplestform, the hemp is simply collected, dried, and placed into a furnace forcarbonization. In other steps, the hemp is ground to a smaller size toallow for more consistent and efficient charring of the material.Consistency of the material is important as the inks produced by themethods herein are optimized with small particles of hemp char that aregenerated in particular sizes within a bell curve. This small andprecise size and distribution of particle sizes in the bell curve allowsfor the material, which is conductive when utilized with a propercarrier, forming a conductive ink.

Pyrolysis

When performing pyrolysis to make the hemp-based carbon of the presentdisclosure, bio-charring temperatures at preferably between about 1100°C. to about 1500° C. and can be performed via batch or continuous flowprocesses. Processed dried hemp is added to a furnace and then heated tomore than 1100° C. and typically less than 1500° C. In particular, theheating process is done under low oxygen conditions to prevent thecomplete combustion of the material, as known to those of ordinary skillin the art. Accordingly, the chamber is filled with one or more inertgasses during the char process. While a temperature of at least 600° C.is sufficient to char the material, it leads to uneven burn of thematerial. More importantly, processing at the low end of the temperaturescale leads to lower amounts of conductivity on its own. Furthermore, insubsequent processing of the material into micron particle sizes, theinconsistent char makes it impossible to effectively grind to asubstantially homogeneous particle size, i.e. a narrow bell curve, withany reasonable yield. Therefore, a temperature above 1100° C. ispreferred.

Accordingly, the process of charring and activating the hemp material isimportant for imparting certain physical properties to the material,specifically toward formation of inks that are conductive. Conductivityis optimized by charring at a temperature of above 1100° C. as detailedin Table 1.

TABLE 1 Comparison of materials for electrical properties Temperature ofFurnace Electrical Material (° C.) Property hemp 600 Weak hemp 900 OKhemp 1100 Good hemp 1200 Good Hemp 1250 Good

In certain embodiments, it may be suitable to activate the char withsteam activation or chemical activation in order to further modify thestructure of the char when it is not initially charred at above 1100° C.These processes, including steam activation or chemical activation, andknown to those of ordinary skill in the art. However, the use of theseprocesses, while functional, reduce the sustainability of the ink.

The hemp-based carbon utilized in the inks of the present disclosure aremade by a unique process. First, as defined in FIG. 1, the activationprocess is preferably charred, wherein the charring is carried out atgreater than 1100° C. in low oxygen conditions. This temperature isdifferent than the prior art, as most bio-charring (charcoal formation)is not carried out at such high temperatures. Indeed, most charring isperformed at between 400° and 600° C. In addition to the difference incharring temperature, the physical characteristics of the hemp plantmake the subsequent processing of the charred material exceedinglydifficult at any suitable yield. Hemp, like any other cellulosic plantmaterial, is simply a structured set of cells. However, charred hemp hasa significantly lower density and weight than other common charmaterials making it more difficult to process into small particles ofuniform size necessary for its use in the inks described herein. Forexample, Table 2 shows several common tree materials and their density,as compared to hemp.

TABLE 2 Density of certain materials Recoverable Density Weight HeatValue of Dry of Dry of Cord Wood Cord (Millions of Species (lb./ft³)(lb.) BTU) Aspen 27 2290 10.29 Cherry 36.7 3121 14 Hickory 50.9 432719.39 Red Oak 44.2 3757 16.8 Hemp 8.74 741 3.33

Process for Generating Substantially Homogeneous Particle Sizes of Hemp

While certain higher density and heavier cellulosic materials are easilycarbonized and then also easily reduced to a uniform and appropriateparticle size, this is not so with the hemp material. More specifically,to process carbonized hemp particle sizes of between 2 and 5 microns isextremely difficult. The low density of the material and the small sizeand consistency of the 2-5 micron carbon desired and necessary forcreating suitable inks makes the milling and classification processextremely difficult. Several processes were tried that resulted invarying levels of success with regard to consistency and also to yield,including hand milling, high energy ball milling, air jet grinding andothers. Importantly, use of a classification system was determined to benecessary to properly sort the hemp-based carbon based on the desiredsize.

In preferred embodiments, the process utilizes a wide range of hempmaterials including: full hemp stalks, chopped full hemp stalks, chippedfull hemp stalk, full hurd, chopped hurd, chipped hurd, ground hurd,separated hurd and fiber, chopped separated hurd and fiber, chippedseparated hurd and fiber, ground separated hurd and ground separatedfiber. However, preferably, the hemp is either primarily hurd material,or a combination of both hemp hurd and hemp fibers. In certainapplications, the combination of the hurd and fibers provides a superiormaterial for conductivity.

Interestingly, we tried several different carriers including aqueousbased and sustainable ink carriers as well as nonsustainable carriers.Plastisol is a nonsustainable carrier base and it can be mixed with thehemp carbon but is not conductive. Several different aqueous bases weretested, each comprising an aqueous vehicle, at least one solid pigmentsuch as TiO₂, or another base pigment. Many of the carriers contain asurfactant, a pH modifying agent, a cosolvent such as a monoalkyl etherof 1-4 carbon alkyl glycols, and other excipients necessary to bind thecarbon, allow the ink to flow, and otherwise serve to stabilize the inkfor printing.

Accordingly, the carrier is preferable an aqueous based carrier, such asMagnaPrint® Aquaflex V2 Neutral, which is an opaque base that can beutilized as a carrier for the addition of a portion of carbonized hemp.There are a number of other commercially available aqueous based clearor opaque bases that can be utilized as the carrier.

In certain embodiments, additional excipients and volatile materials maybe added to the carrier to improve the quality of the ink. For example,it may be suitable to add acids, bases, buffering agents, or salts tothe carrier, as well as certain flowing agents, or bulking agents inorder to optimize the flow of the ink, optimize the viscosity of theink, alter the drying speed and modify the adherence of the ink to amaterial, or modify other properties of the ink. For example, differentalcohols may be added, which are more volatile than the primary watercarrier. Otherwise, a flowing agent, a bulking agent and the like areadded to the carrier to make the final ink product. However, aparticular concern is that while certain components may be utilizedsuccessfully in forming an ink, they defeat the purpose of generating asustainable, ecofriendly water-based ink. Therefore, preferably, the inkcomprises a portion of carbonized hemp, specifically the 3D carbon, andan aqueous carrier.

Inks produced in this manner are “green” as they are formed from naturalmaterials and are themselves biodegradable. This is advantageous whenthe inks are added to biodegradable papers or materials themselves.Furthermore, through selective addition of excipients, the ink is fullyedible, and thus can be used for printing or writing in locations thatneed to be food safe.

In certain embodiments, the 3D carbon material is sold as a pigment,which can be added to a predetermined set of carriers and admixed in asecondary location to form an ink. For example, the product may be apredetermined amount of 3D carbon alone or admixed with one or moreadditional components to yield a dry product. A third party can thentake the dry product and add it to one or more predetermined carriers toyield the ink of choice at the concentrations desired for the finalproduct. A kit would include instructions, suggested formulations andconcentrations, and recommendations for excipients of choice that theend user might want to incorporate. Thus, a user could formulatenonconductive inks or conductive inks as desired.

Therefore, a preferred embodiment comprises a base carrier and carbon,with predetermined amounts of each. The materials are then added basedon a 1-6% by weight of carbon for nonconductive inks, and 14-19% byweight of carbon for conductive inks when printed. By separating thecarbon from the base carrier, the shelf life of the material can begreatly improved, and the individual user can then determine the precisequantity of carbon to add based on the particular use and need.

Milling

Because of the brittle nature of the carbonized material after it hasbeen charred at 1100° C. or greater, it can be directly milled (15) intofine powders having particle sizes in the micron dimensions for suitableuse as a particle in an ink in a mechanical dry or wet milling process.For example, the wet milling process of FIGS. 1 and 3 takes the char andadds it to a shaker with steel balls. In FIG. 3, the hemp is added to afurnace 11, added to a wet mill 15, a solvent is added 61, the materialis milled 62, the material is optionally classified 65, and then addedto a carrier 6, wherein excipients 66, maybe optionally added to formthe master batch of material for ink production 34. In wet milling, aportion of liquid (or a solvent) is added to the shaker, and it isvibrated at between 1 and 100 Hz for a period of between 1 min and 24hours, with between 3 to 30 Hz the most preferred range. FIG. 1describes this process as well, with optional dry milling steps. Each ofthe wet or dry milling will result in rapid reduction of particle sizeinto a particle powder of substantially uniform particle size yieldingthe 3D carbon.

Milling or grinding of the material to a specific classification sizecreates a better product with greater uses than products that do nothave a specific classification size. In certain embodiments, thedistribution of particle sizes within a range may also be defined by anarithmetic mean, arithmetic mode, etc. As used herein, the term“specific classification size” refers to a percentage of particleswithin a certain given point as compared to the classification size. Forexample, a specific classification size of 2-5 microns, means that a setamount of all particles is between 2 and 5 microns. For example, 50% ofall particles. More preferably, a 90%, 95% specific classification size,a 99%, or a greater than 99% specific classification size means that90%, 95%, 99%, or more than 99% of particles are between 2 and 5 micronsin size.

Furthermore, the specific classification size can be further narrowed bydefining a specific micron size and bell curve. For example, a 99%specific classification size of 2-5 microns and a 95% 3.5-micron bellcurve means that 95% of all particles are within 2 standard deviationsfrom 3.5 microns. The bell curve may be a 50%, 75%, 90%, 95%, 99%, ormore than 99% bell curve. In essence, a tighter bell curve gives a batchof particles wherein the particle size is more homogeneous in size thana broader bell curve. Having something be more homogeneous leads to abetter resulting product. In a preferred embodiment, the particles havea 90% specific classification size of between 2 and 5 microns, with a90% bell curve at 2.5, 2.75, 3, 3.25, 3.5, 4.0. 4.5 and 5.0 microns.

The classification process, e.g. as defined in FIGS. 1 and 2, provedespecially difficult to generate a material of less between 2 and 5microns at a suitable yield. To form a material with 90% of particlessmaller than 5 microns, with the average mean particle size between 2-5microns, a screening or classification process is utilized to removeparticles greater than 5 microns after the material is milled and allowfor particles of less than 3 micron. For example, as detailed in FIG. 1,the charred hemp is captured (21), added to a ball mill (or anothermechanical mill) (31). For wet processing, a solvent is added to themill (32), and the material is classified (16). Alternatively,additional excipients (33) can be added before milling or after millingbefore classifying the material (16). In certain embodiments, thematerials are added directly to a master batch for ink production (34),while in other embodiments, the material is captured in desiredfractions (17), i.e. through a classification process, a certain sizeparticle is captured over another size particle. Desired size materialsare maintained and rejected fractions 18 or sized materials are readdedto the ball mill (31) to be remilled.

When dry milling is utilized, the material is added to the ball mill 31,and the material is milled in a mechanical mill and then eitheradditional excipients are added 72, or the material is directly placed73 into a master batch, or the material is added to a classificationstep 16. Thus, when processing, the material can be milled in a wetmedium or a dry medium. In either case, the user may choose to classifythe material or to add it to an ink batch for processing.

Finally, in classifying, the particles are sorted by size. This is aclassification process (16), as defined in FIG. 1. An example of aclassification sieve set is defined by FIG. 2, a first classificationcontainer (41), with a first classification screen (42), a secondclassification container (43), and a second classification screen (44),a third classification container (45), and a third classification screen(46), and finally a fourth container (47), that captures any materialthat falls through the third classification screen (46).

As an example, the first classification screen (42) is 10 microns, thesecond classification screen (44) is 5 microns, and the thirdclassification screen (46) is 2 microns. By adding the charred andmilled hemp to the first container (41), any material greater than 10microns will be captured in the first container (41). This allowsmaterial smaller than 10 microns and larger than 5 microns to becaptured in the second container (43). Material smaller than 5 micronsand larger than 2 microns is captured in the third container (45), andfinally, the material smaller than 2 microns passes through the thirdclassification screen (46) and into the fourth container (47). Otherclassification processes are known to those of ordinary skill in theart.

In preferred embodiments, the preferred particle size is between 1 and 5microns, and more preferably between 2 and 5. The specific range can bedetermined by the classification process. Creation of particles at thissize is optimized for creating inks that are easily printed, e.g.through nozzle or screen printing and possess the necessary propertiesfor color fastness and conductivity.

In order to move to commercial applications, use of grinders may includeair jet grinders, wet processors, small batch high energy ball grinders,dry agitated media mills, and pressure grinding. However, the grindingis mechanical, in order to create a 3D carbon. The grinding processincluded times from about 1 hour to about 24 hours, with all times inbetween.

It is not sufficient to use a process that creates flat, or sheet likecarbon, as these materials result in inferior products and inks. Indeed,when a sample was printed using graphene (a flat, flaky carbon) in thesame carrier as the carbon of the present disclosure, the graphenematerial was more difficult to work with, in that it clogged the finermesh printing screens, it was harder to mix for printing, and uponprinting, it was not a deep black color, but instead had iridescentproperties. Accordingly, for printing of a black material, and for easeof use, the flat carbon proved inferior and was also not a sustainablecomponent of the ink.

For an ink that is intended to transmit electrical signals, it ispreferred to use the material within a carrier that does not increasethe resistance of the char to maintain or enhance electrical properties.Factors that improve electrical conductivity include particle size,structure, and porosity. Small particle size lends to higher electricalconductivity. Where the particles are small and relatively uniform inshape, their surface area is larger than otherwise and allows forgreater contact between particles to generate or store charges. Highstructure means that the carbon agglomerates to form long and branchedchains. Such a structure is ideal for conductive compounds. Higherparticle porosity enables better electrical conductivity, and this isgenerated through increased temperature processing, (i.e. above 1100°C.).

Testing of Printed Ink

In order to test the ink, a number of samples were created withvariations of the quantity of carbon and then tested against varyingscreen sizes, for screen printing onto a cotton material. The methodprinting and the size of the printing mesh changes how much materialflows onto a print surface and this impacts the crocking results as wellas conductivity.

Crocking refers to the rubbing off of color due to abrasion, measured bythe amount of staining on a bleached cotton square. The same is true forwet crocking which uses a wet bleached cotton square. Using the AATCCgray scale for staining, each sample is rated on a scale of 1-5, 1 beingmuch color transfer and 5 being no transfer. Samples containing 1%, 3%,5%, 10%, 15% and 20% Hemp Black carbon by weight were printed on teeshirts using various screen sizes. The smaller the number of the screen,i.e. 60, the fewer and larger the holes in the mesh. The inverse is truefor the larger numbers, such as 156.

Inks were created using MagnaColours Aquaflex V2 Range Neutral as thebase with a portion of carbon ranging from 1, 3, 5, 10, 14, 15, 19 and20% of hemp-based carbon made by the processes as described herein togenerate micron sized carbon. However, other aqueous based carriers,having solids within the carrier and, optionally utilizing a dispersant,a surfactant, solids, and binders, which are soluble in the aqueouscarrier are also suitable.

As detailed in FIGS. 5 and 6, the vertical axis refers to a scale ofcolor transfer, with 1 transferring a lot of color and 5 being no colortransfer. Accordingly, a higher number means that the ink performedbetter than a lower number. The tests on the samples showed that thelower carbon percentages, 1% and 3%, have a consistent superior fastnessto crocking across all screen sizes whether for wet or dry crocking. Asthe percentage of carbon by weight increases, the colorfastnessdiminishes and becomes more inconsistent. The lower percentages performbetter because the base is not overloaded with carbon that it cannothold, decreasing the amount of loose particles on the surface of thesubstrate that will rub/wash off. The larger screen sizes improve thecolorfastness of the sample due to the smaller holes preventing anycarbon not suspended in the aqueous base to pass through onto thesubstrate. At 20% carbon, the material is too loaded and thus the inkdoes not adhere well. Thus, an upper limit of concentration is preferredat 19% carbon.

FIG. 6 details results for wet crocking. In wet crocking, 1% carbon byweight has a consistent superior fastness to crocking across all screensizes. All samples resulted in lower performance during wet crockingcompared to dry due to the usage of a water base. The same carbonpercentage and screen size conclusions made from dry crocking areapplicable for wet crocking.

The conductivity test determined the amount of carbon necessary forconductivity, its response to washing, and also impacts of screen size.The samples were printed with two passes on different screen sizes andtested with a multimeter to confirm or deny conductivity. Samples thatwere conductive were washed in cold water using a high efficiencywashing machine and powdered detergent without optic brighteners. Aftereach wash, samples were measured for conductivity using the samemultimeter with a pass being confirmed at 500 ohm resistance.

FIGS. 7A and 7B depict the result of conductivity testing. For thesamples in FIG. 7A, ink was printed on screen size of 60 with two passesof ink from 1% to 20% carbon (several of the data points are omitted).Each sample was then tested for conductivity before washing, with onewash and with two washes. Interestingly, at 1% and screen size 60, thematerial is unexpectedly conductive. However, upon washing, no samplewas conductive until 14%, when approximately 50% of the samples wereconductive. At 15% carbon by weight, was the first time that a secondwash retained conductivity. Interestingly, the values and conductivityregressed slightly at 17-19 percent.

FIG. 7B details printing using screen sizes 60, 86, 110, 125, and 156.On each screen size, each formula was printed using 1, 2 and 3 passes. Atotal of 1200 samples were created with 240 for each of the screen sizes60, 86, 110, 125, and 156 and an initial pass through samples wasperformed to determine the quantity of samples that were conductive. All1,200 samples were checked for conductivity using a multimeter, whereinthe sample was “conductive” if the multimeter reads below 500 ohms.Interestingly, printing with screen size of 156 reveals that the ink isnot conductive under any of the different weight percentages. It isbelieved that at the 156 screen size, the holes are so small, that thecarbon gets stuck and does not pass through, thus the ink is notconductive, because there is a lack of carbon on the surface. Samplesfor 14-20% are shown stacked with additional washes. So for the screensize 60, 100% were conductive, 75% conductive after 1 wash, and anadditional 75% after 2 washes. This data is continued over the remainingdata points.

Washing greatly impacts conductivity and after one wash, at all screensizes, conductivity is impacted. For the washing tests, each of thetests were washed in high efficiency washing machines on cool cycle. Atone wash, nearly all samples printed with screen size 60 were stillconductive, while all samples printed at 125 screen size were no longerconductive, and x amount of the samples at 86 and 110 screen size wereconductive. Accordingly, where the material needs to be washed, onlysamples at 60, 86, and 110 screen size can be utilized. After a secondand third wash, only the 60 and 86 screen size remained conductive andafter 4 washes, only the screen size 60 remained conductive at more thanfour washes. Accordingly, conductivity is sensitive to the washingmechanism and that if any washing is going to be performed and retainthe conductivity, screen sizes of 60 or 86 are highly preferred.

FIGS. 8A and 8B depict conductivity on the cotton, polyester, andblended materials. After initial testing of concentrations of ink on asample, 15% and 20% Hemp Black carbon formulas were printed on 3different substrates; 100% cotton, 100% polyester and 50% cotton 50%polyester to confirm the prior results. All samples were printed with110 screen size onto the different fabrics and checked for conductivityusing a multimeter. Samples that were conductive were washed in coldwater using a high efficiency washing machine and powdered detergentwithout optic brighteners. After each wash, samples were measured forconductivity using the same multimeter.

FIG. 8B tested the upper limit of the samples, namely with 20% carbon.It is evident from the data that 20% carbon does not perform as well asthe 15% carbon. Evidence shows that there is simply too much carbon.This is in line with the earlier tests which showed that 19% carbon wasthe upper limit for the ink material.

The studies also show that 100% cotton substrate held conductiveproperties longer than 50/50 and 100% polyester. This is because cottonis more absorbent and holds onto the ink better during the wash and drycycles. In nearly all samples the 15% carbon had longer lastingconductivity. This is possibly due to there being less lost carbon thatthe base cannot suspend, making it a more evenly dispersed solution. Amore evenly dispersed solution will have the carbon particles touchingmore consistently, allowing for stronger conductivity. Indeed, thecotton allows for superior absorption of the ink thus locking in thematerial, as opposed to sitting on top of the fibers with syntheticpolyester material. In certain applications, a dispersing agent can beadvantageously added to improve the dispersion of the hemp. A dispersingagent is a dispersant polymer capable of functionalizing the pigment tostabilize the dispersion in the ink. For example a polyester, amethacrylate, or polyethylene oxides.

Therefore, where the material does not need to be washed, conductivitycan be generated at very low concentrations of carbon, if and only if ascreen size 60 (or smaller) is used. Notably, conductivity at 1%, 2,3-10 was generated at screen size 60, and conductivity only appeared forother screen sizes at about 12%, with 100% of prints being conductive at14%.

Furthermore, printing from 14% to 20% yielded conductive materials undermost screen sizes. However, 20% carbon appears to be at or beyond theupper limit of the ink. At the 20% concentration, several problemsoccurred, namely, the carbon percentage impacted the screen at allsizes, making repeated use less reliable due to clogging or otherissues. Furthermore, when washing the 20%, the conductivity fully washesout. When reviewing the 20% carbon, it is clear that the quantity ofcarbon has reached a “saturation” point in the carrier, and that it isdifficult to mix and be supported by the carrier at 20%, and thus yieldsa material that easily washes off, and prints inconsistently. This didnot occur at the 19% concentration. Accordingly, when printing with ascreen size of 86 or 110, which are standard screen sizes, printing aconcentration of between 14 and 19% carbon surprisingly functions thebest to maintain conductivity, and also for overall function of the ink.

However, if a screen size of 60 can be utilized, it was even moresurprising to find that lower concentrations of carbon were suitable.Thus, for single use materials, if conductivity is desired, a lowerconcentration of the material can be utilized to generate conductiveprinting, even as low as 1%. However, the ink was most effective forconductivity when used at, at least 8% carbon, even with screen size of60 and the ink is most effective for conductivity when used between 14and 19% by weight of carbon.

The data confirms that that smaller screen sizes (a smaller screen size,i.e. 60 being “smaller” than 156, means that there are fewer holes inthe screen, and thus the pores in the screen are larger for size 60 thanfor 156) allow for more conductivity. This result is caused by thelarger holes in the mesh allowing for more carbon to be loaded in oneconcentrated area, unlike the smaller holes of the larger screen sizesthat allow for less particles to pass through onto the substrate.However, this has the inverse effect on crocking.

UV Protection

The materials were tested for their ability to block UV rays. UPF standsfor ultraviolet protection factor and measures the sun protection offabrics. A UPF of 50 blocks 49/50 (98%) of UV rays when worn. UVA rayspenetrate the skin deeper, causing long term damage such as skin cancerand wrinkles and comprises 95% of the solar radiation that reachesEarth's surface. UVB rays have a short wavelength and are responsiblefor immediate sunburn.

As depicted in FIGS. 9A, 9B, and 9C, several sample designs were testedfor their UV performance, namely, a grid 9A, a mesh 9B (printing thebackground black and leaving white (open) dots), and an inverse mesh 9C(printing black dots on a white background).

Using the hemp based carbon in a water base blocks high amounts of UVrays when printed on a fabric. The more passes used during printing, themore coverage there is on the substrate, leading to more protection.When printed in various patterns, UV rays are still blocked across theentire surface. The most effective patterns utilize more ink, printedcloser together as detailed in Table 3.

TABLE 3 Ultraviolet Protection Factor % Result Result Formula CarbonRating UVA % UVB % Grid Print 5% 20 97.25 66.26 1 Pass 6% 20 93.85 96.153 Pass 6% 50+ 97.44 98.33 Mesh 6% 50+ 99.65 99.61 Inverse Mesh 6% 3097.87 97.28

The hemp based carbon was also tested against other known pigments andwith other carriers in order to compare the materials. The data andobservations are depicted in Table 4. Notably, the Eco6™ (hemp-basedmaterial of the present disclosure) produces a superior printing atordinary concentrations of the pigment, it is sustainable, and does notrequire an additive to print. Furthermore, the material when used atappropriate concentrations and screen size retains conductivity and alsoadheres well to the printed surface.

TABLE 4 Additives Particle Particle Needed to Sample Size ShapeMixability Visuals Printability Sustainability Print Conductive Eco6 ™1-5 nm Round Easy to mix Blue-gray, Easy to Nontoxic bio- NO YES Water-when not print, prints based pigment Based printed very black andplastisol Ink free solvent Eco ™ 1-5 nm Round Hard to Tar-like, Hard toprint Nontoxic bio- NO NO Plastisol- mix, hard very black based pigmentBased to clean Ink Coconut Undefined Round Does not Shiny and Does notNontoxic bio- YES NO Water- mix well iridescent, print well basedpigment Based coarse and plastisol Ink free solvent Carbon UndefinedRound Easy to mix Finer, Does not Uses fossil YES NO Black very blackprint well fuels and PVC Water- without to produce Based additives orpigment Ink thinners (thicker) Graphene 5 nm Flat Easy to mixIridescent, Easy to print Uses fossil NO YES Water- at lower soft blackat lower fuels and PVC Based percentages percentages to produce Ink(i.e. 5%) (i.e. 5%) pigment

In Table 4, the Eco6™ material was utilized according to the processesas described in this application. In Sample 1, the Eco6™ was admixedwith a water-based solvent. In Sample 2, plastisol was used as thesolvent. In Sample 3, a prior art coconut-based water ink was utilized.In Sample 4, a carbon black water-based ink was utilized. In Sample 5,graphene was utilized in a water-based ink.

Table 4 included several parameters including:

PARTICLE SHAPE: A round particle shape will disperse more evenly than aflat particle.

MIXABILITY: The viscosity of the aqueous solution is affected by howwell the pigment is dispersed. If a pigment clumps within the solution,it will result in an uneven printed color or potentially inhibit thequality of the print.

VISUAL: When producing a true black ink, any iridescence or coagulationwill affect the color and quality of application.

PRINTABILITY: Particles, if not small enough or dispersed evenly, canget stuck in the screen, causing spots in future prints, and creatingtextures. This unevenness can also affect how well the print dry's andcan result in the end product being tacky.

SUSTAINABILITY: Sustainable bio-based pigments such as Eco6™ do notcontain PVC and are free from toxins that are found in carbon blacks.Water based solvents are safe for water ways and are easier to cleanthan plastisol-based solvents. The need to add any additional solventssuch as thinners and viscosity agents, while it may improve quality,reduce sustainability. The ideal combination for a sustainable ink isone that uses bio-based pigments and a water base that results in an inkwhich requires no additional additives in order to perform.

Notably, each of the Samples 2, 3, 4, and 5 fail certain aspects thatare important for a performance ink that is sustainable. For example,the plastisol is hard to print, it is not conductive, it is hard toclean and mix and thus is unusable as an ink material. The coconutwater-based ink did not mix well, after it was printed, it yielded ashiny and iridescent finish and did not print well. This material alsorequired a further additive to enable it to effectively print. Thecarbon black material specifically required the use of additives toprint effectively and it also requires the use of fossil fuels and PVCto produce the pigment, and thus it is not ecofriendly. Finally, thegraphene-based ink is a flat particle carbon, and while it was useful atlower quantities, the material requires fossil fuels and PVC to preparethe pigment.

Therefore, the hemp-based carbon is a superior pigment that possessesunique properties when utilized in an aqueous carrier. The smaller theparticle size, the easier it is for the pigment to be dispersed in theaqueous solution and the more even the color will be. A smaller particlesize also contributes to an improved colorfastness.

The hemp carbon described herein was tested against commerciallyavailable carbon black (a petroleum derivative) for contents of PAH. Thehemp carbon showed a 10% reduction in detected PAH as compared to carbonblack. Furthermore, 33% of the PAH that were detected were less than thereporting limits. This made the hemp derived carbon to be much lower intotal PAH as compared to the petroleum-based materials.

Therefor the hemp-based carbon serves as a unite particle for admixinginto aqueous ink carriers. Specifically, the ink may be formulated forconductivity. The ability for a conductive ink allows for potentialwireless smart textiles and applications within the military and medicalfield. Indeed, the uses of the inks are unlimited. For applicationswhere the material is single use, disposable, and where it may becovered by another layer of material (such that crocking is not anissue), the ink may be conductive at concentrations as low as 1% byweight. To ensure performance, conductive ink is recommended to be inconcentrations of at least 8% when using a screen size of 60, and forlarger screen sizes, i.e. 86 or 110 or larger, then concentrations of14-19% are preferred.

In other embodiments, the hemp black serves as a pigment. Where typicalblack pigment is warranted, the hemp carbon can be utilized at lowconcentrations and yields a safe and effective pigment, specifically atconcentrations of 1% to 6% by weight percent in an aqueous carrier. Thismaterial at those concentrations is easy to use, provides excellentcolor, and is retained on a variety of materials.

Those of skill in the art will recognize that the hemp-based carbon ofthe present disclosure and the inks created thereto are incorporatedinto an ink carrier with the optional inclusion of one or moreadditional excipients. Those of ordinary skill in the art can formulatethe final ink product to meet their specific needs including single useprinting, washable printing, conductive inks, and combinations of thesame. However, use of the hemp-based ink provides an ecofriendlyprinting option that was heretofore unobtainable.

What is claimed is:
 1. A method for making a nonpetroleum-based blackink, said ink comprising an aqueous carrier and a pigment made fromcharred hemp; said charred hemp made by charring hemp stalk at atemperature of at least 1100° C. under low oxygen conditions to create achar; milling said char to create a milled char to between 2 and 5microns; and adding said char to said aqueous carrier.
 2. The method ofclaim 1 wherein the milled char is classified with a classificationsystem having at least one gradient of 2 microns in size and a secondgradient of 5 microns in size; and capturing the material between about2 and about 5 microns in size for addition to the hemp-based ink.
 3. Themethod of claim 1 wherein the milled char is between 1 and 19 weightpercent of the total weight of the ink.
 4. The method of claim 3 whereinthe milled char comprises between 1 and 5 weight percent of the ink tofunction as a pigment and between 14 and 19 weight percent wherein theink is conductive when screen printed with an 86 to 110 size screen. 5.A method of making a conductive hemp-based ink comprising: carbonizing aportion of hemp in a furnace, said furnace being flushed with nitrogenand then heated from 25° C. to greater than 1100° C., holding thetemperature of greater than 1100° C. for at least 60 minutes;maintaining nitrogen flow over the heating and hold times to maintain alow oxygen environment; removing the hemp from the furnace and coolingit to room temperature; milling the cooled hemp to a reduced particlesize and classifying the milled hemp, obtaining a fraction from theclassified hemp wherein 95% of the milled hemp is between 2 and 5microns in size; combining the classified hemp with an aqueous carrierto form the conductive hemp-based ink.
 6. The method of claim 5 whereinthe conductive hemp-based ink comprises between 1 and 19 weight percentof the weight of the ink and is printed using a size 60 printing screen.7. The method of claim 5 wherein the conductive hemp-based ink comprisesbetween 14 and 19 weight percent of the weight of the ink and is printedusing an 86 to 110 size printing screen.
 8. The method of claim 7wherein the conducive hemp-based ink is washable and retainsconductivity after washing.
 9. The method of claim 5 wherein 99% of themilled hemp is less than 5 microns in size.
 10. The method of claim 5further comprising adding at least one solvent to the aqueous carrier,wherein the solvent evaporates faster than water.
 11. The method ofclaim 5 wherein the carrier further comprises an excipient selected fromthe group consisting of: a buffering agent, a resin, a humectant, afungicide, a surfactant, a biocide, a bulking agent, a dispersingpolymer, and combinations thereof.
 12. The method of claim 5 wherein themilling step is a wet milling process.
 13. The method of claim 12wherein the wet milling process comprises addition of a solvent added toa milling chamber with cooled hemp at a ratio of hemp to aqueous solventfrom 10:1 to 1:10.
 14. The method of claim 12 wherein the solventutilized in the wet milling process is a nonaqueous solvent.
 15. Themethod of claim 12 wherein the solvent utilized in the wet millingprocess is an aqueous solvent.
 16. The method of claim 12 wherein theink further comprises a linear or branched chain alcohol.
 17. The methodof claim 16 wherein the liner or branched chain alcohol is a C₁-C₁₀alcohol.
 18. A sustainable ink comprising an aqueous carrier and anonpetroleum-based carbon pigment made from hemp char; said hemp charproduced by charring hemp at at least 1100° C. under nitrogen gas for aperiod of at least 60 minutes; and wherein said hemp char is milled toyield a milled char; wherein the milled char is classified using aclassification system to yield a fraction of classified char between 2and 5 microns in size; wherein the classified char is added to thecarrier at between 1% and 20% of the total weight of the ink.
 19. Thesustainable ink of claim 18 wherein the ink is conductive when printedwith a 60 screen size and at a concentration of at least 1 weightpercent.
 20. The ink of claim 18 wherein the ink is suitable for screenprinting with a size 60 screen, and wherein the classified charcomprises between 1 and 6 weight percent of the weight of the ink, whichyields a nonwashable conductive ink.
 21. The ink of claim 18 wherein theclassified char comprises between 14 and 19 weight percent of the weightof the ink, and wherein the ink is washable upon screen printing with ascreen size of between 86 and 110 and remains conductive after washing.